(1) Field of the Invention
This invention relates to a method for determining the presence of peroxides in fluids, and more particularly to a method for determining trace quantities of peroxides in fluids by measurement of radioactivity.
(2) Description of the Prior Art
Oxygen is omnipresent and while oxygen is essential for the sustenance of aerobic life, several undesirable phenomena are encountered in life associated with the presence of oxygen. For example, rancidity in food; rusting and crusting of metal, plastic and wooden surfaces; occurrences of certain age dependent diseases, such as retinal degenerations, arthritis, cataracts, cardiac injury as well as a number of other age dependent disabling manifestations. The mechanism through which oxygen brings about such a multitude of effects is complex and not truly understood. An initiating event, in most cases, is the conversion of rather sluggishly reactive oxygen to a reactive species, such as superoxide, hydrogen peroxide, hydroxyl radical, etc., extremely potent oxidants. The formation of superoxide and hydrogen peroxide are considered one of the primary events in oxygen acting as such a potent oxidant.
Superoxide is a very unstable free radical and dismutates rapidly in the presence of moisture to hydrogen peroxide. In the case of nonaqueous substances, such as fatty acids, lipid peroxides can be formed. It is important to know when superoxides and consequently the peroxides are likely to form, and, if so, in what quantities or amounts to anticipate and/or possibly avoid or minimize factors that lead to the adverse oxidative consequences thereof. Thus, it is crucial to have a highly sensitive method for peroxide determination, even if present in only "trace" or very low amounts.
In one of the presently used methods, the peroxide is measured in accordance with the following reaction (1); EQU H.sub.2 O.sub.2 +2KI+H.sub.2 SO.sub.4 ---- 2H.sub.2 O+K.sub.2 SO.sub.4 +I.sub.2 ( 1)
The amount of iodine liberated can be determined by complexing it with starch or by consumption of reagents consuming I.sub.2 (iodine); sodium thiosulphate being a common reagent. The method, however, is only applicable for amounts greater than 10.sup.-6 moles/liter of hydrogen peroxide. In addition, the method suffers from the disadvantage that atmospheric oxygen oxidizes iodide into iodine thereby providing a higher value than a true result. Thus, determination of the end point becomes imprecise.
In another method, peroxide is determined by its catalytic decomposition and measuring electrometrically or gasometrically liberated oxygen. Such method is again not sensitive below millimolor levels and suffers from lack of uniformity (in electrometric determination). In addition, in low concentration of the peroxide, catalase is very sluggish in its ability to catalyze the peroxide decomposition.
Certain methods employing fluorescence measurements though applicable at micromolar levels require separation of the already existing fluorophores in the samples. The procedure involved therefore decomposes the peroxide. Furthermore, the exogenous fluorophores used are toxic and carcinogenic.
In most natural situations, particularly in native and experimental biological and nutritional situations, the availability of material for analysis is also very small and the peroxide content in such materials is also very small or present in only trace amounts. Consequently, the determining of the peroxide content in such situations has hitherto been essentially impossible.